CADLAB.io

CADLAB.io is a cloud-based hardware development platform which provides engineers with an enhanced version control system and collaboration tools for hardware design. Based on Git, one of most popular version control systems for software, it allows you to keep native PCB design files in a repository and view, compare and comment on any part of a PCB in a browser.
CADLAB.io can be easily integrated with GitHub and this extension adds a button to each schematic or board layout file in your GitHub repository, so that you can view or compare circuit revisions right from the GitHub project page.